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Fuel Pump Issue - Ghost in the Machine?

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  #1  
Old 04-20-2018, 03:03 PM
ClintJohn
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Default Fuel Pump Issue - Ghost in the Machine?

Hi All,

I have a 95 Dakota V8 Magnum Club Cab with an 80+ litre gas tank, producing results that are apparently stymying more than one pro mechanic. A little back story: I don't remember precisely when but more than 5 years ago the fuel gauge began, on a full tank and without any other performance issues, to waffle between full and half until the fuel in the tank got to about half and then the gauge would read correctly, without a waffle, down to empty.

Fast forward to about 6 months ago, the original fuel pump started to fail and I had to get under the truck and tap it with a hammer to get myself to a mechanic. Got it in to the shop and started with the cheapest fuel pump from Lordco which worked as far as drive-ability was concerned but the gauge read a quarter tank when it was full and the yellow low-fuel indicator didn't work (it lit up when the fuel gauge read half full).

The mechanic and Lordco both honoured their warranties. An apparently better model of pump was installed which produced similar results (truck drove but fuel gauge and low-fuel indicator didn't work properly). So, the mechanic and their supplier, replaced the pump again and again, similar results occurred. I took it back in, the mechanic made some adjustments, told me to fill it up, and let them know one way or the other, if I got anything different. I didn't, but decided that what was happening was good enough for me as I could still drive and instead of using the fuel gauge I relied upon the trip odometer to tell me when it was time for a refill.

This situation continued for, like I said, about 6 months and the following has, in the last two fill-ups, occurred: As I accelerated to highway speed the performance began to fail like it was lacking fuel; bogging down, just like when I was having the original fuel pump issues. I was able to make it to a gas station noting the trip odometer at 350kms which is less than the 400+ at which I was previously accustomed to filling up. The tank only took around 60 litres (a quarter less than its full capacity). I reset the trip odometer and drove away, resolving to check out what happens the next time the odometer hit the same reading.

This time, after experiencing no issue in performance other than the gauge still not working, the trip odometer reads 330kms when the same thing happens the engine sucking for fuel etc... I made it to the gas station, filled up and drove the next three quarters of an hour on the highway, without an issue, home.

Yesterday, I phoned my mechanic and all they had for me (I get it but don't want to believe it) was that there is a ghost in my truck. So, here I am on the forum as a last ditch effort to figure out this "ghost" mostly because I would like to not have this problem but also because I have this (less and less firm) belief that trucks don't have such things.

Any assistance would be greatly appreciated. Sincerely and with gratitude,

Clint
 
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  #2  
Old 04-20-2018, 05:24 PM
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HeyYou
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Do you still have the cheap lordco pump in there? If so, I would pull it, and spend the money on something better. Delphi, or Denso...... I really dislike the el-cheapo fellers, as they rarely work right, and just don't last.
 
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Old 04-20-2018, 07:53 PM
onemore94dak
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I wasted some effort because I did not understand why the gauge was not working. Turns out the previous owner had installed a new pump with the float rod pointing the wrong way. I ended up with a broken rollover valve and finally replaced the whole pump unit with a used one straight out of a 96 or 98 v8. I have the 94 3.9. I have the new pump and assembly sitting in a bag somewhere just in case. The rod points to the front of the truck. There is a fix with another brand rollover valve in the FAQ section and IDK but to agree with HeyYou on the quality of the pump. Note the fuel pump and fuel pump assembly at the link https://www.rockauto.com/en/catalog/...646,fuel+&+air
 
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Old 04-20-2018, 10:30 PM
ragged89
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Originally Posted by onemore94dak View Post
I wasted some effort because I did not understand why the gauge was not working. Turns out the previous owner had installed a new pump with the float rod pointing the wrong way. I ended up with a broken rollover valve and finally replaced the whole pump unit with a used one straight out of a 96 or 98 v8. I have the 94 3.9. I have the new pump and assembly sitting in a bag somewhere just in case. The rod points to the front of the truck. There is a fix with another brand rollover valve in the FAQ section and IDK but to agree with HeyYou on the quality of the pump. Note the fuel pump and fuel pump assembly at the link https://www.rockauto.com/en/catalog/...646,fuel+&+air
Do you have any reason to suspect there could be debri in the tank? Any enemies, lol? I say that because said debri might accumulate around the tank filter, eventually impeding flow, until you fill up again (or bang on the tank), thereby stirring up the contents and clearing the filter. Another possibility is that the pickup on the replacement pumps is too low; when the tank is full the weight of the fuel deforms the bottom of the tank enough to allow fuel to flow, but as the tank empties it blocks the intake on the pickup. Venting is important too, does the tank sound like its sucking air as you open the gas cap? These are long shots, but if they relate to something you've noticed, maybe.

More likely its the pump, as HeyYou and OneMore94Dakota suggested.
 

Last edited by ragged89; 04-20-2018 at 11:01 PM.
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Old 04-20-2018, 10:52 PM
onemore94dak
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Originally Posted by ragged89 View Post
Do you have any reason to suspect there could be debri in the tank? Any enemies, lol? I say that because said debri might accumulate around the tank filter, eventually impeding flow, until you fill up again, thereby stirring up the contents and clearing the filter. Its a long shot I know.
I'm not the Original Poster but that sounds like it could possibly be the problem.
For me I bought it with the gauge not working. The prev owner played dumb which cost me I could have fixed all the problems for half the price if he had just been honest. I was gonna buy it no matter what because it had no rust. Anyway I broke the overflow when I pulled the pump he had put in, I tossed his pump not knowing better. I put a new one from AutoZone in and copied the way he had it and it did not work for fixing the gauge. The pump always pumped. Anyway after a while and doing other things with the truck working out its problems I found out the pump had to be rotated. I did not know about the fix for the overflow valve so I hunted down a used pump that they cut out of a tank with gas still in it at the yard and sold it to me. That is what I have now and the Autozone pump is sitting I suppose I aught to fix the overflow valve for it so it is ready to go. EDIT- the float arm should run parallel with the tank pointing to the front of the truck. This gives it the room to move through its full range. There are usually 2 gallons left when the fill light comes on.
 

Last edited by onemore94dak; 04-21-2018 at 04:02 PM.
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Old 04-21-2018, 05:31 PM
ClintJohn
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hey there Hey You,

thank you for your reply. yes, the second time i went in to the shop we put a Delphi in i think.

Also, it has come to my awareness that the truck's ghost may be a PCM issue...
 
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Old 04-21-2018, 07:54 PM
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May just be a bad relay too...... cheap and easy to swap out.
 
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Old 04-21-2018, 11:49 PM
ragged89
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Originally Posted by onemore94dak View Post
...Anyway I broke the overflow when I pulled the pump he had put in, I tossed his pump not knowing better. I put a new one from AutoZone in and copied the way he had it and it did not work for fixing the gauge. The pump always pumped. Anyway after a while and doing other things with the truck working out its problems I found out the pump had to be rotated. I did not know about the fix for the overflow valve so I hunted down a used pump that they cut out of a tank with gas still in it at the yard and sold it to me...
Yep, I managed to break my roll-over valve too, lol. I need to do that fix, thanks for bringing that entry in the FAQ to my attention, I missed it.
 
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Old 04-22-2018, 10:34 AM
ClintJohn
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Originally Posted by onemore94dak View Post
I wasted some effort because I did not understand why the gauge was not working. Turns out the previous owner had installed a new pump with the float rod pointing the wrong way. I ended up with a broken rollover valve and finally replaced the whole pump unit with a used one straight out of a 96 or 98 v8. I have the 94 3.9. I have the new pump and assembly sitting in a bag somewhere just in case. The rod points to the front of the truck. There is a fix with another brand rollover valve in the FAQ section and IDK but to agree with HeyYou on the quality of the pump. Note the fuel pump and fuel pump assembly at the link https://www.rockauto.com/en/catalog/...646,fuel+&+air
Thank you for the link OM94D. According to the pro-mechanic, he made sure the pump was installed correctly all 3 times he had to address it and considering I don't have the means or know-how/confidence, to check it myself, I have to go with a reasonable assumption that he did what he said competently. MY last conversation with the mechanic resulted in him now leaning toward the PCM/ECM/TCU which has been discontinued in the 95 Dakota. HeyYou spoke of a relay as well though i'm not clear what he's referring to there... researching...
 
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Old 04-22-2018, 10:38 AM
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PCM controls the fuel pump via a relay in the pdc. (assuming the dakota is similar to the full-sized trucks.) So, not getting power to the pump may be caused by a bad relay, or the pcm not controlling the relay......
 
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